The present invention relates to an inverter device including upper and lower arm switching elements, each provided with a plurality of power elements connected in parallel, electrodes, and a substrate, on which the power elements and the electrode are mounted.
Japanese Registered Utility Model No. 3173511 discloses a semiconductor device (inverter). Upper and lower arms each include an element group formed by a plurality of parallel-connected elements. The element groups are for U, V, and W phases and arranged on a main circuit substrate. Positive and negative input electrodes and output terminals for U, V, and W are arranged on the main circuit substrate.
Referring to FIG. 7, element groups G1 to G6, which form the upper and lower arm switching elements, are arranged on a main circuit substrate 200 between a positive input electrode bus bar 201a and a negative input electrode bus bar 202a. Output electrode bus bars 203, 204, and 205, a positive relay electrode 201b, and a negative relay electrode 202b are arranged between adjacent ones of the element groups G1 to G6, which form the upper and lower arms. The input electrode bus bars 201a and 202a, the relay electrodes 201b and 202b, and the output electrode bus bars 203, 204, and 205 each have a length in the longitudinal direction that is shorter than each of the element groups G1 to G6. Current flowing through power elements has a tendency of flowing to an output electrode through the shortest path. The power element that is far from a terminal connection portion of an output electrode in each element group is separated by a long distance from the bus bar and the relay electrode. This lengthens the current path. Thus, the lengthened current path increases the inductance from the power element arranged at the end of each element group to the bus bar and the relay electrode.